The first full body diffusible iodine‐based contrast‐enhanced computed tomography dataset and teaching materials for a member of the Testudines

Abstract

Diffusible iodine‐based contrast‐enhanced Computed Tomography (diceCT) is now a widely used technique for imaging metazoan soft anatomy. Turtles present a particular challenge for anatomists; gross dissection is inherently destructive and irreversible, whereas their near complete shell of bony plates, covered with keratinous scutes, presents a barrier for iodine diffusion and significantly increases contrast‐enhanced CT preparation time. Consequently, a complete dataset visualizing the internal soft anatomy of turtles at high resolution and in three dimensions has not yet been successfully achieved. Here we outline a novel method that augments traditional diceCT preparation with an iodine injection technique to acquire the first full body contrast‐enhanced dataset for the Testudines. We show this approach to be an effective method of staining the soft tissues inside the shell. The resulting datasets were processed to produce anatomical 3D models that can be used in teaching and research. As diceCT becomes a widely employed method for nondestructively documenting the internal soft anatomy of alcohol preserved museum specimens, we hope that methods applicable to the more challenging of these, such as turtles, will contribute toward the growing stock of digital anatomy in online repositories.

The SmARTR pipeline: a modular workflow for the cinematic rendering of 3D scientific imaging data

“…Enhanced by segmentation of anatomical regions of interest and virtual volume sectioning operations, DVR algorithms facilitate a detailed appreciation of complex anatomical structures and spatial relationships within biological samples. Indeed, volume rendering is crucial not only in medical and veterinary diagnostics 96–107 , pre-operative investigations 108–116 , and post-operative follow-up 114,117–120 but also in diverse qualitative and quantitative analyses widely employed in scientific disciplines such as paleontology 121–125 , evo-devo 29,126,127 , ecology 47,128–132 , and zoology 28,30,36,48,49,133–139 . However, although traditional DVR implemented through ray casting technology can generate aesthetically appealing images, it relies on simple lighting and local illumination techniques that hinder the production of realistic representation of 3D data 140–142 .…”

“…Commonly used contrast agents, including Iodine (I2) (either dissolved in ethanol (I2E) or methanol (I2M), or in the form of aqueous Lugol solution (I2KI)), phosphotungstic acid (PTA), phosphomolybdic acid (PMA), and osmium tetroxide Macrì & Di-Poï 2024 4 (OsO4), exhibit distinct diffusive potential, toxicity profiles, and varying degrees of affinity for enhancing soft tissue contrast [39][40][41][42][43] . Owing to their low toxicity, high diffusion rate, contrastenhancing potential, and the ease of removal from specimens, iodine solutions are widely used as soft tissue staining compounds for large biological sample µCT imaging 28,30,[44][45][46][47][48][49][50] . Larger molecules such as PTA or PMA provide excellent soft tissue contrast but permeate samples at a slow rate 37,39,43 , making them suitable for staining smaller or poorly keratinized specimens such as earlystage vertebrate embryos or exposed internal organs [51][52][53][54][55][56][57] .…”

“…Non-invasive techniques like photogrammetry and surface scanning capture detailed morphological information of the outer surface of samples 25 , while X-ray microcomputed tomography (µCT) and magnetic resonance imaging (MRI) reveal their intricate internal structure 25,26 . These techniques are increasingly employed to support qualitative and quantitative morphological analyses in living organisms [27][28][29][30][31][32][33][34][35][36] . Recently, µCT digital imaging has gained momentum due to improved scanner availability, cost-effectiveness, and superior micrometer-level spatial resolution compared to ordinary MRI 25 .…”

Increasing the impact of vertebrate scientific collections through 3D imaging: The openVertebrate (oVert) Thematic Collections Network

“…In preparing a specimen for diceCT, it is submerged in an aqueous iodine solution, also known as Lugol's solution, that passively diffuses through the tissues. The length of time required to reach optimal saturation varies depending on the size of the specimen as well as its surface area to volume ratio, density of external tissues (e.g., carapace of turtles; Gray et al 2024 ), amount of muscle mass, reproductive stage, pathological issues, and the size of the staining vessel or concentration of staining solution. Although the visual effects of diceCT on a specimen are reversible, the process does alter the specimen at the chemical level.…”

Interactive three-dimensional atlas of the mineralized skeleton of the sand tiger shark Carcharias taurus

“…These practices have been applied extensively to model and illustrate the anatomy of classic experimental animals such as mice for some time now [13,14]. In recent times, these techniques have made their way into the fields of comparative anatomy and organismal biology, and rapid advances in visualization techniques [15] have created a boom in digitalized anatomical studies [16][17][18][19].…”